(a) Field of the Invention
The present invention relates to a mechanism for use in an internal combustion engine comprising a crank shaft and at least one cam shaft, in order to progressively vary the angular relationship of each cam shaft relative to the crank shaft when the rotational speed of this crank shaft increases or decreases.
(b) Brief Description of the Prior Art
It is known that the pistons moving up and down inside the cylinders of an internal combustion engine are connected to a crank shaft and work in time or at given internal with respect to each other according to a predetermined angle or a multiple of this angle.
It is also known that the inlet and exhaust valves of an internal combustion engine are operated by a set of rotating cams mounted onto a cam shaft which is connected to, and driven into rotation by the crank shaft. These cams are positioned all around the cam shaft at different angles that are determined by the relative position of the corresponding pistons inside the cylinders. As a result, a given valve is set to open during each cycle of the motor, at a predetermined time which is set once for all in the cycle.
It is further known that to advance or to delay the openings of the inlet and exhaust valve with respect to the relative position of the pistons inside the cylinders may improve the power torque produced by the engine at different speeds and, therefore, the efficiency of this engine. Such a variation in the "timing" of the inlet and exhaust valves opening and closing, however, is not very easy to achieve.
Up to now, the car manufacturers have come up with two different solutions to the above mentioned problem, which are either to adjust the timing to achieve maximum power torque at low speed, or to adjust this timing to achieve maximum power torque at high speed. Other solutions have also been proposed to devise an internal combustion engine that would give a maximum power torque at any speed (see Canadian patent No. 1,202,850 and U.S. Pat. Nos. 2,260,983; 2,279,413; 2,281,883 and 4,502,425). However, all the mechanisms that were proposed so far for this purpose, are not satisfactory because of their structural complexity and/or their substantial cost.